The present invention relates to mechanical means for deploying sonobuoys in the water, and more particularly to a compliant suspension system for supporting a sonobuoy sensor at an extended underwater depth with improved wave-motion isolation.
In the deployment of sonobuoy devices in the water, it is critical to optimum acoustic performance to suspend an associated acoustic sensor, usually a hydrophone, in a stable position at a predetermined depth below the water surface. Typically suspended from a buoyant float using a compliant cable member, the acoustic sensor is generally sensitive to vertical motion imparted through the cable member by surface waves affecting the float. This vertical wave-motion, particularly when imparted to very sensitive hydrophones, can obscure a desired acoustic target signal, and, as a result, wave-motion isolation of the submerged hydrophone is essential for providing effective acoustic surveillance.
Wave-motion isolation of the submerged hydrophone has generally been provided using a compliant member, typically a cable of an elastic material, to suspend the hydrophone from the surface float at a substantially fixed vertical level regardless of the frequency and amplitude of wave movement acting on the float. Coupled with mass dampers as required, these compliant suspension cables of elastic material, such as surgical rubber, have frequently been used to provide satisfactory wave-motion isolation for relatively light sonobuoys having submersible hydrophone units of small wet weights of less than about 10 pounds. However, with the increased use of heavier, active sonobuoys having hydrophone units of wet weights in the range of 30-40 pounds or greater, such elastic cable materials have proven to be cumbersome and inefficient, generally requiring the use of tubing of a very large diameter as the compliant member to support the larger wet weights. Unless a very extended length of such tubing is employed as the suspension cable for the larger hydrophone units, the wave-motion isolation provided is significantly degraded due to the relatively high spring constant that results from the nonlinear elasticity typical of many of these materials. Since the suspension systems of current sonobuoys are typically required to be packaged within a limited volume, the wave-motion isolation provided by the larger, heavier buoys using such compliant cable designs has generally been inadequate. More recently, alternative spring-powered suspension systems have been devised to support a variety of submersible loads. However, such spring-powered systems have also failed to provide sufficient wave-motion isolation to the heavier submersed units primarily because of the characteristically high spring factors of these systems at increased loading.